Deuteronomy 18:20-22 (New International Version)

²⁰ But a prophet who presumes to speak in my name anything I have not commanded him to say, or a prophet who speaks in the name of other gods, must be put to death."

 ²¹ You may say to yourselves, "How can we know when a message has not been spoken by the LORD ?" ²² If what a prophet proclaims in the name of the LORD does not take place or come true, that is a message the LORD has not spoken. That prophet has spoken presumptuously. Do not be afraid of him.